Prepare the Achiote Rub. Mix the achiote seeds with the orange juice and vinegar and soak 1 hour to soften them.
Using a molcajete or mortar and pestle, crush the achiote seeds with a little of the soaking liquid.
Transfer the seeds and soaking liquid to a blender and add the remaining rub ingredients; blend to a paste. Reserve 2 tablespoons of the paste for cooking with the tomatoes.
Rub the pork cubes with the Achiote Rub and set aside.
Heat oil in a heavy skillet over medium heat. Add tomatoes, onions, and the reserved 2 tablespoons of Achiote Rub. Fry for about 3 minutes and set aside.
Preheat oven to 350 degrees. Have a large, heavy Dutch oven ready.
Using tongs, carefully sear the banana leaf over an open flame until flexible.
Line the Dutch oven with the banana leaf and arrange the pork cubes on the leaf. Cover the pork with the tomato mixture, folding the banana leaf over the top. Cover and cook in preheated oven for 2 to 2½ hours, basting occasionally with juices from the bottom of the pot.
Remove from the oven and transfer to a serving platter. Garnish with Cebollas Rojas en Escabeche and serve with Arroz Blanco.
NOTE: If using prepared achiote paste instead of achiote seeds, skip the soaking and crushing step. Simply mash the paste with the orange juice and vinegar and then transfer the mixture to a blender.
Variation: Substitute 4 pounds chicken pieces for the pork. Brown in a skillet with a little oil. Proceed as directed.